Specialization, Speciation, and Radiation

The Evolutionary Biology of Herbivorous Insects

Kelley Tilmon

Publication Year: 2008

The intimate associations between plants and the insects that eat them have helped define and shape both groups for millions of years. This pioneering volume is a comprehensive, up-to-date treatment of the evolutionary biology of herbivorous insects, including their relationships with host plants and natural enemies. Chapters focus on the dynamic relationships between insects and plants from the standpoint of evolutionary change at different levels of biological organization—individuals, populations, species, and clades. Written by prominent evolutionary biologists, entomologists, and ecologists, the chapters are organized into three sections: Evolution of Populations and Species; Co- and Macroevolutionary Radiation; and Evolutionary Aspects of Pests, Invasive Species, and the Environment. The volume is unified by the idea that understanding the ecological framework of the interactions between herbivorous insects and their host plants is fundamental to understanding their evolution.

Cover

Title Page, Copyright, Dedication

CONTENTS

CONTRIBUTORS

PREFACE

This book examines the evolutionary biology of herbivorous
insects, including their relationships with their host
plants and natural enemies. It is a compendium pulling
together many aspects of evolutionary study at different
levels of biological organization, from individuals to clades.
The inspiration for this book was a symposium I organized
for the 2003 annual meeting of the Entomological
Society of America, in memory of the late Thomas K. Wood, ...

PART I: Evolution of Populations and Species

Understanding the physiological and behavioral mechanisms
underlying host-plant specialization in holometabolous
species, which undergo complete development with a pupal
stage, presents a particular challenge in that the process of
host-plant selection is generally carried out by the adult stage,
whereas host-plant utilization is more the province of the larval
stage (Thompson 1988a, 1988b). Thus, within a species,
critical chemical, physical, or visual cues for host-plant identification ...

2. Evolution of Preference and Performance Relationships

Natural selection should favor female phytophagous insects
that have a preference for ovipositing on resources where
their offspring will have the highest fitness (Dethier 1959a,
1959b; Singer 1972; Jaenike 1978). This assertion has been
termed the naïve adaptationist hypothesis (Courtney and
Kibota 1990). This hypothesis has been tested by measuring
oviposition preference and offspring performance in a wide
range of interactions, and contrary to initial expectations a ...

3. Evolutionary Ecology of Polyphagy

The evolutionary ecology of polyphagy by phytophagous
insects has been overshadowed by an intense focus on the
evolutionary ecology of their host specificity. This bias
reflects the preponderance of host specificity in phytophagous
insects (reviewed by Weis and Berenbaum 1989
and Novotny and Basset 2005) and its fascinating consequences
for community structure and evolutionary diversification.
Truly, the study of host-specific herbivores has provided ...

4. Phenotypic Plasticity

Phenotypic plasticity is the ability of an organism, a single
genotype, to exhibit different phenotypes in different environments
(Fig. 4.1A). Such plasticity is nearly ubiquitous in
nature and occurs in various animal and plant phenotypes,
including behavior, physiology, and morphology. Phenotypic
plasticity may be observed as both adaptive and nonadaptive
responses to the biotic or abiotic environment,
though we focus on adaptive responses in interacting ...

5. Selection and Genetic Architecture of Plant Resistance

Basic and applied research programs can both benefit by
approaching concerns regarding resistance to herbivores
from a perspective centering on natural selection and
genetic architecture of resistance. In natural systems,
quantification of selection, determination of genetic correlations
with other traits, and evaluation of genetic architecture
(i.e., estimation of additive and nonadditive
genetic effects) can enhance our ability to predict the evolutionary ...

6. Introgression and Parapatric Speciation in a Hybrid Zone

Hybridization has been recognized by some as a potent evolutionary
force that rapidly can generate new (novel) gene combinations
for adaptive evolution and speciation (Arnold 1997;
Burke and Arnold 2001; Schluter 2001; McKinnon et al.
2004). However, others have historically viewed it as a minor
evolutionary force (barring allopolyploids in plants) or simply
as a local or transient type of evolutionary noise or dead end
(Rhymer and Simberloff 1996; Schemske 2000; Barton 2001). ...

7. Host Shifts, the Evolution of Communication, and Speciation in the Enchenopa binotata Species Complex of Treehoppers

8. Host Fruit-Odor Discrimination and Sympatric Host-Race Formation

Biodiversity is an inherent outcome of evolution. Despite
substantial progress toward discerning the nature of the
evolutionary processes shaping and maintaining biodiversity,
critical questions still remain. For example, what traits
promote rapid speciation and how do they originate? Are
certain groups of organisms more diverse than others and, if ...

9. Comparative Analyses of Ecological Speciation

For much of the twentieth century, the study of speciation
had two major emphases. One was evaluating the geographic
circumstances under which speciation occurred, and
specifically whether geographic isolation (allopatry) was
required (Mayr 1942, 1947; Bush 1969; Futuyma and Mayer
1980; Coyne and Orr 2004). The other was deciphering the
genetic architecture of speciation, that is, the roles played by
chromosomal translocations, and the kinds, numbers, linkage ...

10. Sympatric Speciation: Norm or Exception?

Host-specific herbivorous insects have inspired speculation
about sympatric speciation at least since the 1860s, when
Walsh (1864) described the now famous host races of the
apple maggot (Berlocher and Feder 2002). Even Ernst Mayr,
who lamented that “sympatric speciation is like the Lernaean
Hydra which grew two new heads whenever one of
its old heads was cut off,” admitted that “host races [of phytophagous
insects] are a challenging biological phenomenon ...

PART II: Co- and Macroevolutionary Radiation

Insects and flowering plants are among the most diverse
macroorganisms on earth, and their mutual interactions
provide little doubt that each group is in part responsible
for the other’s diversity (Hairston et al. 1960; Ehrlich and
Raven 1964; Strong et al. 1984; Novotny et al. 2006). However,
exactly how diversification of flowering plants has
affected the diversity of insects, and vice versa, is not well
understood for the vast majority of plant and insect ...

12. Selection by Pollinators and Herbivores on Attraction and Defense

Interactions between plants, their herbivores, and their pollinators
are thought to have led to the diversification of
both plants and insects. Historically, studies of plant-herbivore
and plant-pollinator interactions have occurred independently.
Research at both micro- and macroevolutionary
levels has focused on the evolution of plant resistance in the
context of herbivory, and on floral traits in the context of
pollination. For example, researchers have long recognized ...

A fundamental question in evolutionary biology is how
adaptive radiation proceeds on continents, where most of it
occurs. The question is most pressing when insects are considered,
especially in phytophagous taxa, which represent
over 25% of terrestrial biodiversity. Each taxon has, no
doubt, followed a unique trajectory through time, but unifying
themes should reveal some general patterns and
processes, even if the answers recognize that with different ...

Biologists have long sought an answer to the question,
“What determines species diversity?” Indeed, this question
is one of only 25 key questions featured in the 125th
anniversary issue of Science that were intended to expose
critical gaps in scientific knowledge (Pennisi 2005). A
Nature article by Emerson and Kolm (2005a; but see also
Cadena et al. 2005; Emerson and Kolm 2005b) suggests that
species diversity itself might help to promote speciation.
Put ...

15. The Oscillation Hypothesis of Host-Plant Range and Speciation

From a humble beginning in the early Cretaceous,
angiosperm plants have quickly conquered the earth so
that they now make up one of the most ubiquitous and
species-rich groups (Crane et al. 1995; Wikström et al.
2001; Stuessy 2004; Friis et al. 2005). Likewise, the pioneer
insects that once colonized this novel resource have multiplied
to such an extent that they have become an ecologically
dominating group in all terrestrial ecosystems (Mitter ...

16. Coevolution, Cryptic Speciation, and the Persistence of Interactions

We are faced with three seemingly conflicting observations
regarding the diversification of plant-feeding insects. Insects
can evolve at astoundingly rapid rates when confronted
with new selection pressures, as shown in hundreds of studies
in recent decades. Nevertheless, most insect lineages
remain highly conservative in the range of species with
which they interact. Occasionally, though, insects make
great phylogenetic jumps, even jumping between eudicotyledonous ...

17. Cophylogeny of Figs, Pollinators, Gallers, and Parasitoids

Cophylogeny provides a framework for the study of historical
ecology and community evolution. Plant-insect cophylogeny
has been investigated across a range of ecological conditions
including herbivory (Farrell and Mitter 1990; Percy et al.
2004), mutualism (Chenuil and McKey 1996; Kawakita et al.
2004), and seed parasitism (Weiblen and Bush 2002; Jackson
2004). Few examples of cophylogeny across three trophic levels
are known (Currie et al. 2003), and none have been studies ...

18. The Phylogenetic Dimension of Insect-Plant Interactions: A Review of Recent Evidence

The dramatic expansion of research on insect-plant interactions
prompted by Ehrlich and Raven’s (1964) essay on
coevolution focused at first mainly on the proximate mechanisms
of those interactions, especially the role of plant secondary
chemistry, and their ecological consequences. Subsequently,
in parallel with the resurgence of phylogenetics
beginning in the 1970s and 1980s, there arose increasing
interest in the long-term evolutionary process envisioned ...

PART III: Evolutionary Aspects of Pests, Invasive Species, and the Environment

19. Evolution of Insect Resistance to Transgenic Plants

“If Darwin were alive today the insect world would delight and
astound him with its impressive verification of his theories of
survival of the fittest. Under the stress of intensive chemical
spraying the weaker members of the insect populations are
being weeded out” (Carson 1962). When Rachel Carson wrote
that insightful passage in Silent Spring, evolution of insecticide
resistance had been documented in about 100 species of pests.
In the ensuing 30 years, the number jumped to more than 500 ...

20. Exotic Plants and Enemy Resistance

The increasing movement of organisms to new regions by
humans is enabling species to breach natural dispersal barriers
that normally constrain their geographic distribution.
Oddly enough, despite being introduced to areas that may
be very different from their home region, some exotics
become spectacularly more successful in evolutionarily
novel environments than in areas in which they evolved.
How some exotics come to dominate these new habitats, ...

What are the causes of bouts of rapid evolution and selective
sweeps in the field, and what proportion of such
changes in managed or “pristine” landscapes are nowadays
anthropogenic? Evolutionary events may occur independently
of environmental change, as when a mutation or
hybridization confers increased fitness in existing environments
or when an immigrant arrives in a population suffering
from inbreeding depression. Alternatively, evolution ...

23. Conservation of Coevolved Insect Herbivores and Plants

It goes without saying that one cannot consider the conservation
of plants without thinking about their relationship
with the creatures that eat them—and herbivorous insects
have long been among the worst enemies of the global flora
(Becerra 1997, 2003, 2005). And as anyone who has worked
extensively with butterflies or other herbivorous insects can
tell you, the distribution, abundance, and phenology of
food plants are absolutely key to understanding the dynamics ...

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